The pyrolysis kinetics of cellulosic fibres, a natural cotton yarn (NCY) and a mercerized cotton yarn (MCY), has been explored with a modified first order global analysis method (FOG), via a series ...of non-isothermal experiments, using thermogravimetric analysis (TGA). The modified FOG analysis routine was developed to overcome discrepancy in heating rate and the difference between exact results and approximations in integrals. The intrinsic pyrolysis activation energy, with temperature range tending to zero, was found to be independent of heating rate and approximation used, giving average values of 153 ± 2 kJ/mol for NCY and 192 ± 7 kJ/mol for MCY. This proves the applicability of the reported analysis routine under the conducted TGA measurements. The reasons for different values were hypothesized to be the difference in chemical composition and crystalline structure. The findings provide a new approach in the investigation on pyrolysis kinetics of biomass and factors impacting their pyrolytic behaviour.
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•Process analysis of pyrolusite reduction by biomass pyrolysis is reported.•Thermodynamic analysis confirmed the pyrolusite reduction by biomass pyrolysis.•The kinetics and thermodynamics of ...reduction process were calculated.
As an alternative energy source for fossil energy, use of biomass pyrolysis to reduce pyrolusite is of great significance for energy conservation, emission reduction and environmental protection. Kinetics and thermodynamics of reducing pyrolusite using biomass pyrolysis was studied using thermogravimetric analysis analysis. Five non-isothermal methods, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Distributed Activation Energy Model, Starink and Friedman, were employed to calculate the pyrolysis kinetics and thermodynamic parameters. The results showed that pyrolusite reduction by biomass pyrolysis can be divided into four stages: drying stage (30–175 °C), rapid pyrolysis reduction stage (175–350 °C), slow pyrolysis reduction stage (350–680 °C) and char formation stage (680–900 °C). The apparent activation energy, reaction enthalpy, Gibbs free energy and entropy change of pyrolusite reduction by biomass pyrolysis was calculated ranges from 170 to 180 kJ/mol, 164 to 174 kJ/mol, 136.97 to 137.25 kJ/mol and 45.67 to 61.91 J/mol·K, respectively. This work provides theoretical basis and practical guidance for the reduction of pyrolusite by waste corn stalk.
The large waste potential of biomass, which is used extensively industrially, is a problem that needs to be solved both environmentally and economically. In this context, the conversion of these ...wastes into valuable solid products by thermochemical conversion processes is considered a very important alternative. In this study, it was aimed to examine the pyrolytic behavior of Aloe vera leaf waste, determine the pyrolysis kinetic parameters and characterize the biochar obtained as a result of pyrolysis at different temperatures. The pyrolytic behavior of this waste at temperatures between 25 and 600 °C and heating rates of 5, 10, 20 and 40 °C min−1 were investigated by thermogravimetric method. The pyrolysis kinetic parameters of these wastes were calculated using the Kissinger-Akahira-Sunosa (KAS) and Flynn-Wall-Ozawa (FWO) methods. According to the results obtained, the pyrolysis of Aloe vera waste took place in 3 stages (moisture removal, devolatilization and char formation) and approximately 65% of the mass was removed from the structure. The activation energy values calculated by KAS and FWO methods for the devolatilization and char formation stages were found to be approximately 185 kJ mol−1 and 335 kJ mol−1, respectively. According to the kinetic and characterization results obtained, it has been understood that Aloe vera leaf wastes are a very suitable source for biochar production and biochar obtained can be evaluated in different areas such as adsorption, agriculture and combustion.
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•Pyrolysis reaction consisted of three stages and 65% of the mass was removed.•As pyrolysis temperature increased, the similarity to the coal structure increased.•Pyrolysis activation energy values were found as approximately 185 and 335 kJ mol− 1•KAS and FWO are suitable methods for specifying the pyrolysis of Aloe vera waste.
•Pyrolysis kinetics of beech wood is analyzed using model-free and -fitting methods.•Pyrolysis measurements conducted in two thermogravimetric analyzers are compared.•Effect of final temperature of ...pyrolysis on the kinetic parameters is analyzed.•Final temperature affects kinetic parameters at the end of the pyrolysis process.•Better recuperation of thermogravimetric curves is obtained with model-free methods.
The pyrolysis kinetics of beech wood was analyzed using model-free and model-fitting methods. Experimental measurements of the pyrolysis process were conducted in two thermogravimetric analyzers (TGA), a TG 209/2/F from Netzsch and a TGA Q500 from TA Instruments, which were found to have a similar precision in the establishment of the present heating rate. Two experimental procedures were employed: (i) introducing samples which were pre-dried externally before the experiments were executed and (ii) internal (in situ) drying of the samples in the TGA via a special temperature program below 150 °C which preceded the pyrolysis process.
The kinetic parameters were derived (i) using several model-free methods, namely Kissinger method, isoconversional methods, a simplified Distributed Activation Energy Model (sDAEM) and, (ii) using a model-fitting method via a five-step reaction model which calculates the differential thermogravimetric (DTG) curves at different heating rates; the calculated DTG curves were further analyzed by Kissinger’s method to obtain overall kinetic data.
The kinetic parameters were found to be different in the two experimental procedures. Also, they turned out different when the assumed end temperature of the pyrolysis process was varied. This is because the pyrolysis of slowly charring solid residues becomes more important with increasing temperature and finally overruns the release of volatiles from the wood samples. For the same experimental procedure and for sufficiently low end temperatures, corresponding to a degree of conversion less than 85%, model-free and model-fitting methods resulted in similar kinetic parameters.
•The effect of phosphorus valence states on combustion behaviors of UPR was analyzed.•Flame retardant UPR achieved UL-94 V0 with only 15 wt% of PBPG.•+3 phosphorus valance of PBEG was more helpful to ...improve flame retardancy of UPR.•The preparation of flame retardant UPR was mainly based on gaseous phase mechanism.
This work analyzes the effect of different valence states in phosphorus structures on thermal stability, pyrolysis kinetics and flame retardancy of unsaturated polyester resin (UPR). Then, the corresponding mechanisms are systematically analyzed. The poly(ethylene phenylphosphonate) (PBEG) and poly(ethylene phenoxyphosphate) (POEG) were synthesized, and the combustion behaviors of UPR, such as pyrolysis, ignition, heat suppression and charring capacity were studied. The phosphorus structures with +5 valence states in POEG was more conducive to formation of carbon layers than that of +3 valence states in PBEG. The better charring capacity made pyrolysis activation energy (Ek) of UPR/POEG different from UPR/PBEG in F-W-O and DAEM fitting methods. The Ek of UPR/POEG was larger than pure UPR at high mass conversions, but Ek of UPR/PBEG was less than pure UPR during entire pyrolysis process, due to different phosphorus-containing pyrolysis products. For PBEG, more phosphorus-containing species existed in gaseous phase to capture H· radicals; By contrast, POEG left more products in condensed phase, promoting the formation of thermally stable carbon layers. Different phosphorus-containing products also affected flame retardancy of UPR. UPR reached UL-94 V0 with only 15 wt% of PBEG, where peak heat release rate (PHRR), total heat release (THR), fire growth index (FGI) were obviously reduced. However, flame retardant efficiency of POEG were lower than PBEG. This indicates that +3 phosphorus valance of PBEG is more helpful to improve flame retardancy of UPR, and the essential reasons have been systematically analyzed. Meanwhile, the selection of high-efficiency flame retardant systems for UPR materials can be based on gaseous-phase mechanism and supplemented by condensed-phase mechanism.
The thermokinetics of sassafras wood pyrolysis were studied via thermogravimetric inverse modeling. Model-free combined with model-fitting methods were used to explore the optimal kinetics. Results ...indicate the obtained averaged activation energy and pre-exponential factor are 215.12 kJ/mol and 8.65 × 1017s−1, while the reaction model in charge is g(α) = -ln(1-α)1/3. In the following, Kissinger-based K–K method was adopted to separate the single reaction kinetics for each pseudo components. The analysis of K–K method provided the basis of the search range for each kinetic parameters. Finally, a new optimization algorithm was put forward, and the multi parallel reactions scheme incorporated into the Grey Wolf Optimization coupled with the Least Squared Fitting procedure was adopted to perform the optimization. The predicted MLR curves based on the simultaneously optimized kinetic parameters fit well with the experimental data not only at heating rates of 10, 20 and 30 K/min, but also at 5 and 40 K/min which were not used in the optimization. Such results indicated the excellent applicability of the optimized parameters and efficiency of the hybrid optimization procedure. Results from the present work could be a guidance for further biomass pyrolysis evaluation under more complex practical scenarios.
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•Model-free combined with model-fitting methods were used for kinetics study.•The most suitable model for sassafras wood pyrolysis was g(α) = -ln(1-α)1/3.•A Grey Wolf Optimization based hybrid fitting procedure was proposed.•Optimization model integrated with TPR schemes improves efficiency and accuracy.
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•Pectin-free quince waste (yield 3.2 wt% db) showed higher reactivity to pyrolysis.•Pyrolysis was well described by a multi-step mechanism for quince waste.•Activation Energy varied ...between 44.22 and 105.39 kJ/mol for the quince waste.•Activation Energy ranged between 27.92 and 115 kJ/mol for pectin free quince waste.
This work aims to study and compare the kinetic and thermodynamic behavior of pyrolysis of quince waste (QW) and pectin-free quince waste (PFQW) after extraction. The pectin extraction with acid treatment had a yield of 3.2 ± 0.1% (dry basis, db). Pyrolysis experiments were conducted in a macro-TG reactor at three heating rates (5, 10, and 15 °C/min) and temperatures in the range 27–900 °C under a nitrogen atmosphere. A better fit of the experimental data was achieved by modeling the reactions by a multi-step mechanism considering three different parallel reactions for thermal decomposition of hemicelluloses, cellulose, and lignin. The results indicated that the Flynn-Wall-Ozawa (FWO) method provided the best R2, MSE, and AAD values. The resulting values of the thermodynamic activation parameters ΔH, ΔG, and ΔS were 53.28–89.36 kJ/mol, 114.54–155.01 kJ/mol, and −0.17–(−0.04) kJ/(mol K) for pyrolysis of QW, and 29.97–90.68 kJ/mol, 99.42–158.86 kJ/mol, and −0.23 – (−0.01) kJ/(mol K) for PFQW. According to bioenergy indicators, PFQW presented good characteristics as a biofuel feedstock due to its high energy density values. The kinetic and thermodynamic parameters indicated greater reactivity of PFQW to pyrolysis compared to QW, showing that in addition to obtaining a product with added value, such as pectin, the extraction process generates a solid residue that is easier to treat under a thermochemical platform. The novelty of the paper focuses on the influence of the pretreatment of quince bio-waste (by extracting pectin compounds) on reactivity to pyrolysis, providing valuable kinetic and thermodynamic information.
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•0D and 1D models were used to model biomass pyrolysis of thermally-thick particles.•A detailed reaction kinetics was employed to model pyrolysis and product components.•Correction ...coefficients were used to derive corrected 0D model from 1D modeling.•The derived corrected 0D model was proved to have the same accuracy as 1D model.•ANN was used to efficiently obtain correction coefficients for wider applications.
In reactor-scale CFD modeling of biomass pyrolysis with thermally-thick particles, zero-dimensional (0D) models coupled with lumped kinetics are commonly used, as they are simple and computationally efficient. However, intra-particle heat transfer, which cannot be directly implemented in 0D models, has significant effects on pyrolysis behaviors of thermally-thick biomass particles. Additionality, lumped kinetics usually fails to predict detailed composition of pyrolysis products. To overcome these issues, a widely-used one-dimensional (1D) model that can directly incorporate intra-particle heat transfer was employed with a detailed pyrolysis kinetics in this work to develop a corrected 0D (Cor-0D) model for accurate CFD modeling of biomass pyrolysis inside thermally-thick particles. Correction coefficients of external heat transfer, particle diameter, and pyrolysis reactions were introduced by comparing predictions of the 1D model with those of the 0D model quantitatively to reflect the effects of respective factors. The comparison demonstrates that if correction coefficients are properly determined, predictions of the developed Cor-0D model are in good agreement with experimental data as well as those of the employed 1D model under various conditions, while the 0D model overestimates mass loss rate and particle heating rate for thermally-thick biomass particles. Considering that correction coefficients are case dependent and determination of their values are tedious, artificial neural network (ANN) was used to correlate correction coefficients as functions of convective heat transfer coefficient, particle size, gas temperature, moisture content, and particle’s dimensionless temperature to derive an ANN-Cor-0D model. Results show that the ANN-Cor-0D model has the same performance as the Cor-0D model.
Recent studies indicate that accurate description of the reaction mechanisms in fast pyrolysis of 1,3,5-trinitro-1,3,5-triazinane (RDX) is still of great challenge. In this work, the pyrolysis ...mechanism of RDX has been investigated by ab initio kinetic calculations and modeling simulations. The potential energy profiles of primary and secondary reactions in RDX decomposition were constructed with B2PLYPD3/CBS//B3LYP-D3/6–311+G(d,p), and the rate constants were obtained from the solution of RRKM/master-equations. The proposed reaction pathways and calculated rate constants were incorporated into a kinetic model. The simulated results illustrate that the decomposition of RDX mainly occurs through its NNO2 bond fission to generate RDXR, whose subsequent decomposition mainly undergoes CH β-scission to form INT175 and the ring-opening reaction to form RDXRO. Interestingly, the less favored initial intermediate, INT175, is predicted to be a major product in the secondary decomposition of RDXR. The incorporation of important channels for key intermediates, such as CH β-scission of RDXR, remarkably affects the decomposing pathways of RDX. Meanwhile, the contribution of bimolecular reactions such as H/O abstraction reactions from RDX by NO2/NO is simulated to be insignificant for the decomposition of RDX under the conditions studied.
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